The use of reinforced concrete columns of various shapes for carrying vertical loads is well known and widely practiced. However, strengthening and/or rehabilitation of such columns is often required to eliminate structural problems resulting from unusual loading, exposure to aggressive environment, aging, inadequate design and/or poor construction. Upgrading of the columns with fiber reinforced polymer (FRP) sheets is a well-known technique for repair and rehabilitation by placing the fibers mainly transverse to the longitudinal axis of the columns.
It has been recognized that the effectiveness of the FRP confinement in delaying and limiting unstable crack propagation depends to a large degree on the stiffness of the FRP jacket. However, it is also well known that the use of FRP confining systems for columns with a rectangular cross section is less effective than on a circular cross section due to a part of the cross sections remaining unconfined and that the effectiveness depends on the sharpness of corners. In addition, it is well known that the confinement provided by FRP to the confined concrete in a rectangular shaped column is reduced as the aspect ratio increases. In fact, the benefit of FRP wrapping in terms of ductility should be neglected if the aspect ratio is more than 1.5.
A U.S. Patent Publication No. 2006/0070338 in the name of Pantelides et al. discloses Shape Modification and Reinforcement of Columns Confined with FRP Composites. As disclosed, FRP composites have a number of advantages over steel, including their high strength-to-weight ratio and excellent durability. The confinement effectiveness of FRP materials for rectangular sections can be improved by performing shape modification such that a rectangular column section is modified into a shape that does not have 90 degree corners such as an elliptical, oval or circular column. An expansive concrete can be advantageously used between the FRP material and the existing concrete in order to post-tension the FRP material circumferentially and improve confinement of the concrete. A finite element analytical model is also disclosed which describes the stress-strain relationship for the FRP-confined columns after shape modification.
Notwithstanding the above, it is presently believed that there is a need and a potential commercial market for an improved shaped modification of wall-like rectangular reinforced concrete columns in accordance with the present invention.